1. Field of the Invention
The present invention relates to multiple substantially identical countershaft, simple change gear transmissions and in particular to multiple countershaft, simple change gear transmissions wherein each of the countershafts is substantially identical and comprises a separate first and second generally coaxial piece rotating at the same rotational velocity and wherein each countershaft assembly is supported by a bearing means at each end thereof and by a third bearing means adjacent the driving connection of the two countershaft pieces.
2. Description of the Prior Art
Simple change gear transmissions, that is, transmissions utilizing a one piece mainshaft, are well known in the prior art. Transmissions utilizing either simple or compound mainshafts in connection with multiple countershafts wherein the mainshaft, the mainshaft gears and/or the countershaft gears are mounted in a radially floating manner relative to the other gears are also well known in the prior art. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,255,644; 3,283,613; 3,335,616; 3,349,635; 3,378,214; 3,500,695; and 3,648,546, all of which are hereby incorporated by reference.
The prior art transmissions, particularly those transmissions utilizing a floating and/or pivoted mainshaft in connection with multiple substantially identical countershafts, have proven to be highly acceptable. However, to achieve a sufficiently large range and/or number of available gear ratios, it has generally been necessary to utilize a compound transmission. Such transmissions generally comprise a main transmission section and an auxiliary transmission section of either the "range" type or the "splitter" type or a combination thereof as is well known in the prior art. Such transmissions are highly effective and commercially successful, especially for use in heavy duty vehicles wherein a large range of ratios is required and/or a large number of individual gear ratios is required. Such heavy duty compound transmissions typically have 9, 10, 12, 13 or more forward gear ratios.
There has, however, developed a need for multiple substantially identical countershaft transmissions having a greater range of ratios and/or a greater number of ratios than is normally available in a simple transmission utilizing one-piece countershafts supported by two bearings as the center-line distances required in prior art simple transmissions to provide same would become too great yet not justifying the somewhat expensive structure and controls required for a compound transmission. The prior art devices have been unable to completely satisfactorily fill this need.
Attempts to fill this need include supporting countershafts by a third bearing intermediate the ends of the countershafts. This has not been satisfactory as a three bearing mount of a one-piece shaft requires greater than normal manufacturing accuracies and/or assuring correct circumferential alignment of the countershaft pieces of a two-piece countershaft assembly upon assembly or reassembly thereof has proven difficult.
Another attempt to fill this need involves the use of compounded countershafts as is seen in U.S. Pat. No. 4,152,949 hereby incorporated by reference. While such a simple transmission utilizing compounded countershafts is believed to be highly advantageous, the required additional structure and expense may not be justified for certain applications.